1. Field of the Invention
The present invention generally relates to surgical methods and an apparatus for explanting bone plates. More particularly, the present invention relates to a method and an apparatus for screw removal from bone plates used in osteosynthesis.
In osteosynthetic treatments of fractured bones so called locking compression plates (LCP) are frequently used. Usually these locking compression plates comprise plate holes for an insertion of bone screws which are configured as combination holes permitting to insert conventional screws or alternatively locking head screws (LHS). These known combination holes are configured as elongated holes having two parts wherein a first part is unthreaded and includes a concave recess and a second part is provided with a conical interior thread. The second part is arranged at one of the two ends of the elongated hole and the interior thread tapers conically towards the underside of the bone plate. Furthermore, the interior thread runs across an arc of more than 180° to firmly receive the conically threaded screw head of the locking head screw. Once implanted the conically threaded screw head of the LHS locks firmly in the correspondingly threaded second part of the combination hole. The concave recess in the first part faces the top side of the plate so as to receive a bone screw having a spherical head thereby allowing the bone screw to be advanced through the plate hole into the bone with an angle relative to the bone plate which is different from 90°.
2. Description of the Related Art
It is known in the art that upon explanting the LCP there is a risk for technical complications which are particularly due to the fact that the LHS could not be loosened because they were jammed in the LCP and/or bonded to the inner surface of the plate hole due to bone/soft tissue ingrowth. If the torque for loosening the locking head screw is too high the screw driver recess in the screw head can become critically damaged or the screw driver tip can break so that the screw driver recess becomes jammed by the broken screw driver tip. In these emergency situations the surgeon usually has special tools available to solve these technical complications. The majority of damaged locking head screws can be removed by using a conical extraction screw driven into the screw driver recess or by drilling off the screw head of the locking head screw. Another procedure currently performed to remove jammed bone screws is to saw the plate apart in the area of the screw hole. However, all of these known procedures are cumbersome and time-consuming.
Thus, there remains a need for an improved method and apparatus for screw removal which allows one to overcome the above disadvantages.